Can anyone help me with firefox and the media player add-on/plug in ?

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I want to watch some episodes on abc.com and for some reason the video wouldn't play and it said I need to download something but the puzzling part is that its never happened before and I haven't installed anything that would mess with the program. On my firefox browser it tried to install the program but when the installation window goes to my add-on everything is blank . I also tried to install from another website but no luck. How can I do ? Thanks for you suggest.